This invention relates to a mounting that mounts a cab body on a chassis frame in a wheeled land vehicle. More particularly, the invention relates to an improvement for limiting shearing stress created in a fastener that fastens a bracket of the mounting to a member of the cab body when large relative acceleration between the cab body and the chassis frame occurs in a fore-aft direction in a vehicle. Such large accelerations can occur during extreme frontal impacts of the vehicle with other objects.
In the event of frontal impact of the vehicle with a foreign object, relative acceleration of the body on the frame in the fore-aft direction may occur. Severe frontal impacts may create large acceleration forces. The component of such forces in the fore-aft direction creates shearing stress in the fastener of a known mounting that will be discussed later in connection with FIGS. 1 and 2. The fastener material has a characteristic maximum allowable shearing stress. Severe unchecked forces may create stress levels exceeding the maximum allowable shearing stress for the fastener. The fastener is therefore at risk of shearing and the vehicle is at risk for potentially adverse consequences of such shearing.
For minimizing the risks, the fastener can obviously be made larger. But size may become a concern, not only from the standpoint of available space in the vehicle, but also from the standpoint of assembly operations in a vehicle assembly plant where vehicles are mass-produced on an assembly line. For example, not all vehicles coming down the line may require larger fasteners. In that case, multiple tools, such as air wrenches, must be available for installing the differently sized fasteners, and that introduces assembly line complications that involve extra time, space, and expense.
It is therefore seen desirable if such complications could be avoided. It is toward that objective, for one, that the present invention is directed.
One general aspect of the invention relates to a wheeled land vehicle comprising a chassis frame and a cab body mounted on the chassis frame by a mounting that comprises a frame-side bracket attached to a chassis frame member and a body-side bracket attached to a cab body member. A fastener attaches one of the brackets to the corresponding member and experiences shearing stress as one of the chassis frame and the cab body accelerates relative to the other with a component of motion along a fore-aft dimension of the vehicle. A structure that includes an elastomer through which the two brackets are associated in an assembly relationship allows limited motion between the brackets in multiple dimensions accompanied by deformation of the elastomer, one of the multiple dimensions being the fore-aft dimension of the vehicle. The other bracket comprises a formation that, when the elastomer is not being deformed by acceleration forces, is spaced a predetermined distance apart along the fore-aft dimension of the vehicle from the member to which the one bracket is attached by the fastener. The formation is also disposed for abutment by the member to which the one bracket is attached by the fastener for arresting motion of the cab body relative to the chassis frame when a component of acceleration force along the fore-aft dimension of the vehicle displaces the cab body relative to the chassis frame sufficiently to reduce to zero the spacing between the formation and the member to which the one bracket is attached by the fastener. The arrest occurs before shearing stress in the fastener exceeds the maximum allowable shearing stress for the fastener.
Another general aspect of the invention relates to a mounting for a cab body on a chassis frame of a wheeled land vehicle comprising a frame-side bracket for attachment to a chassis frame member and a body-side bracket for attachment to a cab body member. One bracket comprises a face containing a hole and spaced apart, mutually confronting, vertical flanges at opposite sides of the face. A first fastener passes vertically through the hole in the face to attach the one bracket to the corresponding member. A structure through which the two brackets are associated in an assembly relationship comprises an annular, deformable elastomeric bushing having a central axis that is horizontal and also comprises an outer circumference disposed in a hole in the other bracket such that the central axis of the bushing is perpendicular to the fore-aft dimension of the vehicle. A second fastener passes horizontally through aligned holes in one flange of the one bracket, the bushing, and the other flange of the one bracket perpendicular to a fore-aft dimension of the vehicle. The other bracket comprises a vertical wall that confronts, and is in spaced relation to, the horizontal face of the one bracket when the elastomeric bushing is in an undeformed condition.
Another general aspect of the invention relates to a method of limiting shearing stress in a first fastener that fastens one of two brackets of a mounting to one of a cab body member and a chassis frame member in a wheeled land vehicle caused by relative acceleration between the two members having a component of motion along a fore-aft dimension of the vehicle. The mounting comprises a structure through which the two brackets are associated in an assembly relationship. The structure comprises an elastomer and a second fastener that allow limited motion between the brackets in multiple dimensions accompanied by deformation of the elastomer, one of the multiple dimensions being the fore-aft dimension of the vehicle. The method comprises providing the other bracket with a formation that is disposed to be abutted by the one member to which the one bracket is fastened by the first fastener for arresting motion of the one member relative to the other member when a component of acceleration force along the fore-aft dimension of the vehicle displaces the one member relative to the other member. The arrest occurs after a predetermined amount of relative motion that assures that shearing stress created in the fastener does not exceed the maximum allowable shearing stress for the fastener.